how many btu's do i need?
we are trying to get an accurate estimate on the number of btu’s needed for a new boiler in our 4 story 17 ft. wide brownstone. how does one determine this and who should we talk to? so far, the range we’ve heard is huge & we want to obviously get the most efficient, high…
we are trying to get an accurate estimate on the number of btu’s needed for a new boiler in our 4 story 17 ft. wide brownstone. how does one determine this and who should we talk to? so far, the range we’ve heard is huge & we want to obviously get the most efficient, high performance setup.
I have 4 story semi detached 17×50=3400 sq st and a 150kbtu steam system. Many heating contracters overestimate on the theory that there will be no complaints of inadequate heat if they do (they don’t have to pay the bills.)
So get a heating estimate and look it over carefully. otoh, use 150 as a starting point; if you’re better insulated than I am (none in roof and one side detached,) you may even need less.
Thanks, MP.
AAIB,
My experience, probably for the reasons I’ve listed in my first post, is that just about every heat calculation I do reveals a significantly over-sized existing boiler.
Rules-of-thumb are of course never a substitute for real figuring, but when the building has lots of glass or is on a corner lot or has excessively high ceilings, etc….the heat loss may go as high as 40 btu psf. Rarely ever more.
op again…thanks everyone (and sorry master plumber!)
as long as we’re on the subject-where should i be looking to buy a furnace? home depot?
Go to heatinghelp.com. Good advice there and they may even have a calculator for this sort of thing.
30 BTU/sf?
So a 3500 sf townhouse clocks in at 105K?
Non-sarcastic question: I see 180K+ for townhouse boilers usually; is all of Brooklyn oversized?
Yeah, you might’ve mentioned that before I typed up my heating dissertation.
(just kidding)
Rule of thumb is 30 BTUs per square foot of living space.
op here. i feel like a damn fool. i realized that i meant to say that we are replacing our oil furnace with a gas furnace (forced air, not radiators) and are trying to determine the # of btu’s needed.
any new advice as i sit here with my foot in my mouth?
thanks.
If you’ve got a circulating hot water heating system the boiler should be sized to the heat loss of the home.
That means measurements are needed to calculate the area of the house and then the type of materials that make up the envelope of the building are taken into account. The result is the amount of heat needed to replenish that amount which is naturally lost by the building through air infiltration, convection and radiation.
If you’ve got a steam heating system, disregard all of the previous calculations and have the radiators measured.
The production of steam is measure in square feet.
The measurements of a radiator equate to a specific value also expressed in square feet.
A replacement boiler’s steam production must be equal to the system’s ability to convey and condense steam by matching those two numbers.
That means anyone who tries to sell you a steam boiler without first measuring every radiator and heat emitter connected to the system has no idea what size boiler you need.
Replacing the boiler with what’s there now can be a costly error.
Most old boilers also made hot water for the occupants’ sinks and showers and so they were sized for that extra heating load which is no longer necessary as many of us use tank-type water heaters now.
In addition to that, many steam systems were installed shortly after 1917 (the year of the Spanish flu) and were sized to heat the building with the windows open.
Again, these original boilers were grossly oversized for the job they need to do today and it’s been sort of customary for lazy heating contractors to use the put-back-what’s-there method of heat calculation.
Just about every boiler I am called to replace in this area has gone this route through the years.
After doing the right math I find most boilers to be oversized by 40%-70%, sometimes much more, consistently.
Using the right size boiler may mean operating at 200,000 BTU (833 square feet of steam) per hour rather than 320,000 (1,333 sq. ft./hr) BTU per hour.
There’s significant fuel savings there.
Having this service, called an EDR (Equivalent Direct Radiation) Calculation, performed is likely to cost you some money but it may be your last chance before you make a commitment to inefficiency that may last 20 years or more.